microautofagia

Microautophagy is a cellular degradation process in which cytosolic components are directly captured by lysosomes or vacuoles and degraded inside these organelles. Unlike macroautophagy, which uses double-membrane autophagosomes to sequester cargo before lysosomal fusion, microautophagy relies on invagination, protrusion, or septation of the lysosomal or vacuolar membrane to engulf cytosolic material and form intralysosomal vesicles or to degrade cargo directly within the lysosome.

Mechanisms and modes of microautophagy can vary. In membrane invagination, portions of the lysosomal membrane bend inward and pinch off to enclose cytosolic material. In vesicle-mediated microautophagy, small vesicles bud into the lysosome from the limiting membrane. The process can be non-selective, particularly under nutrient limitation, or selective through cargo-recognition mechanisms involving adaptor or receptor proteins and, in some systems, ESCRT machinery that mediates membrane scission.

Distribution and regulation of microautophagy are widespread across yeast and animal cells. Some forms are dependent on Autophagy-related (Atg) proteins in certain contexts, while others may proceed independently of the core macroautophagy machinery. Microautophagy operates in concert with other autophagic pathways and can complement macroautophagy, especially when macroautophagy is limited or stressed.

Physiological roles include general turnover of cytosolic components, quality control of damaged proteins, and participation in adaptive responses to nutrient stress. Although less understood than macroautophagy, microautophagy contributes to cellular homeostasis and has been implicated in various research contexts and disease models, prompting ongoing study of its cargo selectivity and regulatory mechanisms.